1. Field of the Invention
The present invention relates to a propylene-based copolymer, a producing process thereof and film comprising the copolymer. More particularly, the present invention relates to a propylene-based copolymer having a practical transparency and excellent low-temperature heat sealability and rigidity, to a producing process thereof and to film comprising the copolymer.
2. Description of Related Arts
Polypropylene resins are excellent in transparency, heat-resistance, food hygiene and the like, and therefore, widely utilized in fields such as film, sheet and the like. Recently, with increase in bag production speed in packaging fields of foods and the like, materials having a low temperature heat sealability are desired.
As a polypropylene having a low temperature heat sealability, for example, JP-2882237B discloses a copolymer excellent in low temperature heat sealability obtained by copolymerizing propylene and an xcex1-olefin other than propylene, or propylene, ethylene and an xcex1-olefin other than propylene with a Ziegler-Natta catalyst, wherein the propylene content, ethylene content, xcex1-olefin content and the content of 20xc2x0 C. xylene soluble part are restricted to specified ranges. However, the random copolymer having a good low temperature heat sealability, namely being low in heat sealing temperature, is insufficient in rigidity, and therefore, further improvements have been required.
An object of the present invention is to provide a propylene-based copolymer having a practical transparency, and excellent low temperature heat sealability and rigidity.
Another object of the present invention is to provide a process for producing the propylene-based copolymer.
Still another object of the present invention is to provide film comprising the copolymer.
Other objects and advantages of the present invention will be apparent from the following description.
Namely, the present invention relates to a propylene-based copolymer obtained by copolymerizing propylene with ethylene and/or an xcex1-olefins having 4 or more carbon atoms in the presence of a polymerization catalyst in a first step to produce a copolymer having a content of the xcex1-olefins of 1 mol % or more and less than 15 mol % and an ethylene content of 5 mol % or less in amount of 1 to 30% by weight as a copolymer component (A), and subsequently copolymerizing propylene with ethylene and/or an xcex1-olefins having 4 or more carbon atoms in a second step or later steps to produce a copolymer having a content of the xcex1-olefins of 15 to 30 mol % and an ethylene content of 5 mol % or less in amount of 70 to 99% by weight as a copolymer component (B), to a process for producing the copolymer, and to film comprising the same.
The present invention will be illustrated in detail below.
The propylene-based copolymer of the present invention is a copolymer obtained by copolymerizing propylene with an xcex1-olefin having 4 or more carbon atoms and/or ethylene in a first step to produce a component(A), and subsequently copolymerizing propylene with an xcex1-olefin having 4 or more carbon atoms and/or ethylene in a second step or later steps to produce a component (B). The component (A) is preferably a copolymer component obtained by copolymerizing propylene with an xcex1-olefin having 4 or more carbon atoms, and the component (B) is preferably a copolymer component obtained by copolymerizing propylene with an xcex1-olefin having 4 or more carbon atoms.
The content of the component (A) is from 1 to 30% by weight, preferably from 5 to 30% by weight, more preferably from 5 to 20% by weight. The content of the component (B) is from 70 to 99% by weight, preferably from 70 to 95% by weight, more preferably from 80 to 95% by weight. The sum of the components (A) and (B) is 100% by weight.
When the content of the component (A) is less than 1% by weight, properties of polymer powder formed in copolymerization may be deteriorated to decrease productivity, and when the content of the component (a) is over 30% by weight, the low temperature heat sealability of a film made of the copolymer may be insufficient.
The content of the xcex1-olefin having 4 or more carbon atoms contained in the component (A) is 1 mol % or more and less than 15 mol %, preferably 5 mol % or more and less than 15 mol %, more preferably from 5 to 10 mol %. When the content of the xcex1-olefins having 4 or more carbon atoms contained in the component (A) is less than 1 mol %, processability may be insufficient, and when 15 mol % or more, it may be difficult in some cases to stably produce the component (A).
The content of the xcex1-olefin having 4 or more carbon atoms contained in the component (B) is from 15 to 30 mol %, preferably from 15 to 25 mol %. When the content of the xcex1-olefin having 4 or more carbon atoms contained in the component (B) is less than 15 mol %, the low temperature heat sealability of film may be insufficient, and when over 30 mol %, the rigidity of film may decrease.
The ethylene content in the component (A) is 5 mol % or less, preferably 3 mol % or less. The ethylene content in the component (B) is also 5 mol % or less, preferably 3 mol % or less. When the content of ethylene in the component (A) or (B) is over 5 mol %, film may be whitened with the lapse of time and the rigidity thereof may decrease.
Herein, the sum of propylene and an xcex1-olefin having 4 or more carbon atoms and ethylene is 100 mol %.
Examples of the xcex1-olefin having 4 or more carbon atoms include, for example, 1-butene, 2-methyl-1-propene, 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 2-ethyl-1-butene, 2,3-dimethyl-1-butene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 3,3-dimethyl-1-butene, 1-heptene, methyl-1-hexene, dimethyl-1-pentene, ethyl-1-pentene, trimethyl-1-buene, methylethyl-1-butene, 1-octene, methyl-1-pentene, ethyl-1-hexene, dimethyl-1-hexene, propyl-1-heptene, methylethyl-1-heptene, trimethyl-1-pentene, propyl-1-pentene, diethyl-1-butene, 1-nonene, 1-decene, 1-undecene, 1-dodecene and the like are exemplified, and preferable are 1-butene, 1-pentene, 1-hexene and 1-octene, further preferable are 1-butene and 1-hexene from the standpoints of copolymerization property and economy and the like.
As the component (A) or (B), for example, a propylene-1-butene copolymer component, propylene-1-hexene copolymer component, propylene-ethylene-1-butene copolymer component, propylene-ethylene-1-hexene copolymer component and the like are listed, and preferable are a propylene-1-butene copolymer component and propylene-1-hexene copolymer component. The components (A) and (B) may be the same or different in combination of the monomers to be copolymerized.
As the propylene-based copolymer of the present invention, for example, a (propylene-1-butene)-(propylene-1-butene) copolymer, (propylene-1-butene)-(propylene -ethylene-1-butene) copolymer, (propylene-ethylene-1-butene)-(propylene-1-butene) copolymer, (propylene-ethylene-1-butene)-(propylene-ethylene-1-butene) copolymer, (propylene-1-hexene)-(propylene-1-hexene) copolymer and the like are listed, and a (propylene-1-butene)-(propylene-1-butene) copolymer and (propylene-1-hexene)-(propylene-1-hexene) copolymer, and further preferable is a (propylene-1-butene)-(propylene-1-butene) copolymer.
The melt flow rate (hereinafter, sometimes abbreviated as xe2x80x9cMFRxe2x80x9d) measured at 230xc2x0 C. under a load of 21.18N according to JIS K7210 of the propylene-based copolymer of the present invention is not particularly limited, but preferably from 0.1 to 50 g/10 minutes, more preferably from 1 to 20 g/10 minutes, from the standpoint of flowability or film formability.
The MFR of the propylene-based copolymer may be changed by a known method during melt-kneading. For example, a method of adding an organic peroxide to the propylene-based copolymer and the like so far as the object and effect of the present invention are not damaged, are listed.
Production of the propylene-based copolymer of the present invention can be conducted by multi-step polymerization composed of a first step, and a second step or later steps, using a known polymerization catalyst in a known polymerization method except that the copolymer components (A) and (B) are adjusted to the specific ranges described as above.
As the polymerization catalyst, preferably stereoregular polymerization catalysts such as Ziegler-Natta catalysts, metallocene-based catalysts and the like, are preferably listed, and catalysts containing Ti, Mg and a halogen as essential components are more preferable. For example, there are Tixe2x80x94Mg-based catalysts obtained by using a solid catalyst component obtained by combining a magnesium compound with a Ti compound, and catalyst systems obtained by combining the solid catalyst component and an organoaluminum compound, and optionally, a third component such as an electron donative component or the like, and there are exemplified catalyst systems described in JP61-218606A, JP61-287904A and JP07-216017A, and the like.
The organoaluminum compound is not particularly restricted, and preferable are triethylaluminum, triisobutylaluminum, a mixture of triethylaluminum and diethylaluminum chloride, and tetraethyldialumoxane.
The electron donative compound is not particularly restricted, and cyclohexylethyldimethoxysilane, tert-butyl-n-propyldimethoxysilane, tert-butylethyldimethoxysilane and dicyclopentyldimethoxysilane are preferable.
As the polymerization method, there are listed a solvent polymerization using an inert solvent represented by a hydrocarbon solvent such as hexane, heptane, octane, decane, cyclohexane, methylcyclohexane, benzene, toluene, xylene or the like, a bulk polymerization using a liquefied monomer as a solvent, a gas phase polymerization conducted in a gaseous monomer, and the like, and preferable are a bulk polymerization and gas phase polymerization in which post treatment and the like are easy. These polymerization methods may be conducted batch-wise or continuously.
In the process of producing the propylene-based copolymer of the present invention, the polymerization is conducted in multi-stage composed of a first step and a second step (in case of two steps) or a first step and later steps (in case of more than two steps), in the above-mentioned polymerization. The polymerization method of the first step and the polymerization method of the second step or later steps may be the same or different, and preferably, from the standpoints of polymerization activity and easiness of post-treatment, the first step is a step in which polymerization is conducted in the absence of an inert solvent and the second or later steps are a step in which polymerization is conducted in gas phase. Polymerization of the first step and polymerization of the second or later step may be conducted in the same polymerization reactor, or conducted in different polymerization reactors.
As the method of producing the propylene-based copolymer of the present invention, there are listed, for example, a solventxe2x80x94solvent polymerization method, bulkxe2x80x94bulk polymerization method, gas phase-gas phase polymerization method, solvent-gas phase polymerization method, bulk-gas phase-gas phase polymerization method, solvent-gas phase-gas phase polymerization method, bulk-gas phase-gas phase polymerization method and the like, and preferable are a bulk-gas phase polymerization method, gas phase-gas phase polymerization method and bulk-gas phase-gas phase polymerization method.
The polymerization temperature in the first step is not particularly restricted, usually from 20 to 150xc2x0 C., and from the standpoints of productivity and control of contents of the component (A) and the component (B), preferably from 35 to 95xc2x0 C. The polymerization temperature of the second or later steps may be the same as or different from the polymerization temperature of the first step, and is usually from 20 to 150xc2x0 C., preferably from 35 to 95xc2x0 C.
In the method of producing the propylene-based copolymer, catalyst deactivation, de-solvent, de-monomer, drying, granulation and the like as post-treatments may be conducted.
To the propylene-based copolymer, additives and other resins may be added. As the additives, for example, antioxidants, ultraviolet absorbers, antistatic agents, lubricants, nucleating agents, tackifiers, anti-fogging agents, and the like are listed.
As the other resins, for example, polyethylene-based resins, polypropylene-based resins, other polyolefin-based resins and the like are listed.
The film of the invention is a film containing a film layer made of the propylene-based copolymer, and includes mono-layer film of the propylene-based copolymer, multi-layer film having at least two layers and containing the film layer of the propylene-based copolymer, and the like. These films are suitable for packaging film. The packaging film includes, for example, a food packaging film, clothing packaging film, and the like, preferably a food packaging film.
As the method of producing the film of the present invention, there are listed an inflation method, T die method, calender method and the like. And, a method of producing a single film of the propylene-based copolymer, using these methods, and method of producing a multi-layer film containing at least one layer of the propylene-based copolymer and at least one layer of a different resin, are illustrated.
Methods of forming a multi-layer structure, there are listed a co-extrusion molding method, extrusion lamination method, heat lamination method, dry lamination method and the like, usually used. A co-extrusion molding method is preferable from the standpoint of balance of properties such as the low temperature heat sealability, transparency and rigidity of film obtained.